The U.S. Defense Department is denying a report in a publication specializing in defense issues that says insurgents in Iraq are using a new type of improvised explosive weapon that can be shot about 15 meters into the air to attack low-flying helicopters. The report came the day after the latest incident in which a U.S. helicopter went down, with the cause of the crash still under investigation.

A spokeswoman for the Defense Department's special task force on countering Improvised Explosive Devices says no aircraft have been lost to any new 'jumping' weapons, and indeed that there are no confirmed reports of any such weapons being used in Iraq.

At a news conference on Wednesday, the top civilian official in charge of the U.S. Army, Secretary Francis Harvey, had slightly different information from the task force statement issued later in the day. The military calls insurgent bombs IEDs (Improvised Explosive Devices).

HARVEY: "That's an anticipated threat. To my knowledge we, we have not, I don't know if we've seen, we may have seen one of those. But to my knowledge we have not seen a lot of those so far, jumping IEDs.

The officials were responding to a report in the Tuesday edition of Defense News that quotes Brigadier General Edward Sinclair, commander of the Army's Aviation Center in Alabama. The general is quoted as saying such weapons have been used against U.S. army helicopters several times, but he would not say whether they have been effective.

The article says the weapons use proximity fuses and are designed to explode when they come close to a large object, like a helicopter. It says they are used in areas where helicopters frequently fly at low levels, and near the sites of other attacks when medical evacuation helicopters are arriving or departing.

The latest crash of a U.S. helicopter in Iraq came Monday morning north of Baghdad. Witnesses were quoted as saying it was hit by a missile, but U.S. officials say the cause of the crash is still under investigation.

U.S. officials say the majority of U.S. casualties in Iraq are caused by Improvised Explosive Devices, most of them planted along roadsides. Secretary Harvey confirmed that again on Wednesday. The Defense Department recently expanded and upgraded the task force that is working on a variety of technological and intelligence-based methods of combating the primitive but effective weapons.